DEVICE FOR DETECTING ELECTRIC CURRENTS ON OR NEAR ELECTRIC CONDUCTORS

Description

[0001] The invention relates to a device for detecting electrical currents on or near electrical conductors, comprising at least one reed contact as a magnetically responsive switch, which is arranged in such a way that, in the event of a significant current flow through the conductor, the resulting magnetic field triggers the switch and initiates evaluation electronics connected to the switch according to claim 1, as well as the use of such a device for detecting and classifying lightning and overcurrent events according to claim 14.

[0002] A short-circuit indicator for electrical lines is known from DE 2 826 247 C2.

[0003] The short-circuit indicator features a reed switch controlled by the magnetic field of an electrical conductor and an electronic latching circuit. This latching circuit is a flip-flop design that controls both an electronic counter and a clock generator. The clock generator triggers a flashing signal. After a set time, the electronic counter resets the flip-flop circuit and stops the clock generator.

[0004] The reed contact used is arranged in a plane parallel to the conductor in such a way that at the moment of a short circuit a correspondingly large magnetic field is generated, which acts on the reed contact and closes it at least briefly.

[0005] This applies a supply voltage to the input of the flip-flop circuit, causing it to enter the self-holding position.

[0006] Rotating the reed contact around the imaginary longitudinal axis of the housing reduces its sensitivity. This allows the short-circuit indicator to be factory-set to specific, graduated tripping currents, for example, in the range of 200–400 A.

[0007] DE 103 29 223 B9 discloses a short-circuit current sensor which uses the force of the magnetic field of a short-circuit current to close a reed contact which is mounted on a circuit board in such a way that it can be adjusted to a specific trigger current by a rotation between 0 and 90°.

[0008] DE 27 00 995 A1 concerns a monitoring system for an electrical, current-carrying consumer.

[0009] The consumer is, in particular, the brake or taillights of motor vehicles. A magnetic field-dependent switch, which leads to a display device, is positioned within the magnetic field generated by the current flowing through the consumer's supply line. A reed contact is typically used as the switch.

[0010] In a preferred embodiment, the switch is arranged inside a coil formed by the consumer supply line, so that the magnetic field surrounding each individual conductor is superimposed on the adjacent coil windings to obtain sufficient response sensitivity.

[0011] In one of the training courses offered there, the coil and the magnetic field-dependent switch are combined as a single unit, which can be inserted into the supply line of the consumer.

[0012] In the arrangement for the selective tripping of series-connected, selectively started circuit breakers, in which a circuit breaker directly affected by the short circuit outputs a blocking signal to a tripping system according to DE 199 30 089 A1, a protective tube contact is magnetically coupled to each main current path of a downstream circuit breaker and electrically connected to the tripping system of the upstream circuit breaker.

[0013] Preferably, the protective tube contact is arranged near a terminal of the circuit breaker.

[0014] DE 197 33 268 A1 describes a method for detecting overcurrents and short-circuit currents in conductors of a medium- or high-voltage system, as well as a device for carrying out the method. The device has one reed contact per conductor of the system, which is triggered when a magnetic field generated by an overcurrent or short-circuit current occurs, thereby generating a pulse in the device.

[0015] From WO 2017 / 036793, a method for recording lightning current parameters in installations with multiple air terminals and lightning current discharge paths is known. Two different types of lightning current sensors are used for this purpose: a simple lightning current detection sensor for each air terminal, which only provides a yes / no indication of a lightning current event, while a central lightning current measurement sensor is used to distinguish between surge currents and long-term currents.

[0016] German patent application DE 10 2010 038 856 A1 discloses a passive magnetic switch with at least two reed contacts extending in different directions, such that their contact tongues can be moved in different directions to open and close the respective reed contact. The magnetic switch is used to detect magnetic fields in any spatial direction, for example, within the field of influence of a magnetic resonance imaging (MRI) scanner.

[0017] DE 44 30 382 A1 describes an electromechanical switching device with a combination of differential Hall effect sensors, a reed sensor and a welding sensor.

[0018] RU 2 544 282 C1 discloses a method for detecting electric currents in an electrical conductor and a device for this purpose. The device comprises a plurality of reed switches, each arranged at a different distance from the electrical conductor and connected to a microcontroller. The reed switches are arranged such that they only activate with increasing distance at a progressively larger current flowing through the electrical conductor. From the times at which the reed switches trigger (and reopen after the current decays), a polynomial is determined that approximately describes the current waveform. This polynomial is then used to determine the amplitude of the detected current.

[0019] The prior art solutions described above have in common that a reed switch forms the basis of a switch, which can be actuated by a magnetic field. With sufficient magnetic energy, the contact reeds of a known reed switch move into a contact-closing position, with the result that the circuit in which the switch is located is closed. Based on the use of such reed switches, circuits can be monitored and their function signaled. Furthermore, a short-circuit current can be detected by defining the short-circuit current itself as a threshold value whose magnetic field is capable of closing the reed switch.

[0020] From the foregoing, the object of the invention is to provide a further developed device, occupying only a small installation space, for detecting electrical currents on or near electrical conductors with at least one reed contact as a magnetically responding switch, wherein the device is not only able to define a switching state upon reaching a certain current flow in the electrical conductor, but also has the possibility of detecting and evaluating current pulses and thus surge currents, without the need for complex electronic circuits, which are therefore expensive and prone to failure, similar to so-called lightning counters.

[0021] The problem of the invention is solved by a device according to the combination of features according to claim 1 and the use according to the invention as taught in claim 14, wherein the dependent claims represent at least expedient embodiments and further developments.

[0022] Extensive investigations have surprisingly revealed that impulse current magnitudes can be determined and differentiated using a quasi-spatially staggered arrangement of multiple reed contacts, spaced apart relative to an electrical conductor and / or staggered in their sensitivity. Particularly surprising is the finding that not only long-term impulse currents can be detected, but also short-term impulse currents can be evaluated. The device according to the invention also operates reliably in harsh environments and under the influence of mechanical shocks and vibrations, which is surprising with regard to certain applications, such as monitoring lightning strikes in wind turbines.

[0023] Due to their inherent design, reed contacts possess a mechanical inertia that makes reproducible response to extremely short pulse loads unlikely. The observed, defined response of the sensitive contacts, sometimes occurring even during the pulse process, is just as unpredictable as the equally reproducible response of contacts with lower sensitivity or higher mechanical inertia, even well after the pulse load without any further magnetic field present. Furthermore, the overload resistance, especially of the sensitive reed contacts, is surprising. Both pulse currents of < 100 A and small long-term currents can be reliably detected.Even with significantly larger impulse loads up to 250 kA with magnetic field loads that are 1000 times or more above the response voltage, the mechanical components of the respective reed contact are not mechanically destroyed or damaged by the high dynamic forces, so that even after such multiple loads, reproducible detection of impulse currents is possible.

[0024] By positioning the respective reed contact according to the invention and by providing a virtually loop-free connection of the terminals, the detrimental coupling of currents into the contact path can be reduced to such an extent that the necessary sensitive contacts with very low switching currents are not damaged by the induced currents during closing, including any high-frequency contact bounce, by preventing arcing. Sparking can be prevented by additional circuitry of the reed contact. Undesired coupling of currents into the connection loop of the reed contacts can be reduced by active or passive overvoltage protection measures.

[0025] The device according to the invention for detecting electrical currents using reed contacts can be integrated into a so-called intelligent lightning rod or can be a component of such a lightning rod in order to be able to evaluate lightning events.

[0026] According to another application example, the device according to the invention can be used to detect currents in conductors that are part of a building structure and are used as lightning conductors in accordance with EN 62305-3. The reed contacts can also be installed on or near electrically conductive components that are not generally intended for lightning protection, but through which a partial lightning current can flow. Examples include cable car haul ropes, crane support ropes, or similar components. In this respect, it is possible to detect potential damage to such ropes caused by partial lightning currents at an early stage, in order to initiate appropriate measures, such as replacing damaged ropes.

[0027] The galvanic isolation resulting from the use of reed contacts and the distance of the device with its electronic components from the lightning current-carrying conductor enables trouble-free operation over a long period without maintenance.

[0028] Likewise, the device according to the invention can be a component of surge arresters or used to assess the load on surge arresters by integrating the device according to the invention into the relevant current path or assigning it to it.

[0029] The device according to the invention thus represents a cost-effective alternative to otherwise used, complex measuring systems, for example using so-called Rogowski coils.

[0030] The device according to the invention enables a dual function to be achieved in its application by detecting disturbance current pulses, for example based on lightning events, and distinguishing these with regard to pulse shape and pulse duration as well as current level.

[0031] The device for detecting electrical currents on or near electrical conductors therefore uses a reed contact as a magnetically responsive switch, which is arranged in such a way that when a significant current flows through the conductor, the resulting magnetic field triggers the switch and initiates a triggering electronics connected to the switch.

[0032] According to the invention, a plurality of reed contacts are arranged at a predetermined distance to the electrical conductor for the detection of impulse current quantities and the differentiation between long-term impulse currents on the one hand and short-term impulse currents on the other.

[0033] Furthermore, according to the invention, at least one of the reed contacts is provided with a shield to influence the magnetic field acting on the respective reed contact in order to adjust the response behavior.

[0034] The evaluation electronics determine the response and switching times of the respective reed contacts. From the assignment of the determined values ​​to the reed contact, or rather its spatial arrangement and the distance to the electrical conductor, the impulse current magnitude and, from the switching time, the pulse shape can be determined, preferably using a microcontroller.

[0035] According to the invention, not only normally open reed contacts can be used. It is also possible to use normally open reed contacts. Such normally open contacts can be implemented in conjunction with a permanent magnet in such a way that the contact's response behavior is adjustable.

[0036] It is therefore in line with the invention to adjust the response behavior with respect to current discrimination not only by spatially spacing the contacts, but also by using other criteria. The aforementioned shielding is proposed for setting limits to the response behavior of the respective reed contacts. This shielding can be implemented as a metallic sleeve or a metallic layer. For high-frequency processes, for example, metallic sleeves or layers for generating eddy currents based on copper or aluminum materials are suitable. To reduce sensitivity to low-frequency processes, materials with high permeability, such as soft magnetic steels, can be used.

[0037] To utilize both effects, materials with high permeability can be additionally coated with electrically conductive materials, for example, copper. Due to the saturation of high-permeability materials in strong magnetic fields, a staggered arrangement of the shielding materials surrounding each reed contact is advantageous.

[0038] The shielding allows the sensitivity of the reed contacts to be individually adjusted and changed, ultimately making it possible to use standard reed contacts with the same sensitivity and design.

[0039] Due to the limitations of varying spatial distances between the reed contacts and the electrical conductor, alternatively or additionally, normally open contacts of the same design with different opposing magnetic fields can be used. Similarly, normally closed contacts can be used, which, in addition to being distanced, are also shielded against the effects of magnetic fields.

[0040] In one embodiment of the invention, the electrical conductor is part of a lightning current conductor, a lightning rod or a conductive component through which a lightning current can, in principle, flow.

[0041] In another embodiment of the invention, the electrical conductor is a component of a surge current-carrying overvoltage arrester.

[0042] The evaluation electronics include a data storage device in addition to the preferred microcontroller.

[0043] The stored data can be transmitted wirelessly or via wired connections or fiber optics (FO) to a higher-level unit for long-term analysis of impulse currents or long-term currents.

[0044] This makes it possible, for example by integrating a large number of devices according to the invention into complex buildings, to record, store and evaluate loads relating to overcurrent events for site or hazard analysis.

[0045] To ensure continuous, maintenance-free operation of the device, it is equipped with a long-term power supply.

[0046] Because the device according to the invention is usually in a so-called sleep mode and is only activated when overcurrent events occur, only extremely low quiescent currents occur, which lead to desired long operating times without changing a battery or accumulator.

[0047] In one embodiment of the invention, the device according to the invention can also draw energy from the network to which the current-carrying conductor is usually connected.

[0048] The energy required for pulse registration or for operating the evaluation circuit can be obtained from the actual interference or measurement signal, i.e., from the pulse itself.

[0049] An alternative method for generating energy for operations is so-called energy harvesting. This can involve generating energy from movement or by using photovoltaic elements.

[0050] In a further development of the invention, the device includes a radio module for data transmission, wherein, according to the invention, the data transmission is only triggered after a predetermined time period has elapsed following the decay of the last pulse current. In this way, interference-free data transmission is ensured.

[0051] In one embodiment of the invention, at least the reed contacts are fixed on a flat wiring carrier, for example a copper-coated circuit board.

[0052] In a preferred embodiment of the invention, the angular position of the groups of reed contacts relative to the electrical conductor is fixed and not variable in order to achieve reproducible measurement results.

[0053] Furthermore, according to the invention, a housing for receiving the components of the device is designed, which has an end face or side surface that is provided with means for marking the position and / or for fastening the electrical conductor.

[0054] In this way, when the device is used or mounted on or near an electrical conductor, a correct correspondence between the field formed around the conductor when current flows and the reed contacts located in the housing is ensured.

[0055] Because the housing does not need to have any openings for receiving or passing through the electrical conductor, it can be designed for the highest levels of protection, i.e. for use outdoors and under critical environmental conditions.

[0056] In a particular embodiment of the device according to the invention, it is designed to be arranged on or near the lightning conductor cables of rotor blades in wind turbines. A downstream counting device can record the number, intensity, and pulse shape of lightning current events in order to determine whether the so-called receptors located on the surface of wind turbine rotor blades are already excessively stressed or melted, thus allowing for scheduled maintenance or repairs.

[0057] The device according to the invention can also be used to monitor and assess potential lightning strikes on conveyor ropes, for example, those of cable cars. The detection of lightning currents in the conveyor ropes is achieved by appropriately arranged and designed sensors with reed contacts, as described in the teaching. When lightning currents or partial lightning currents are detected, a message is sent to a higher-level control unit. This allows the system to determine whether an inspection of the conveyor rope is necessary and, if so, to initiate a shutdown of operations. The detection of long-term currents is particularly problematic in such applications. Long-term currents are crucial for understanding melting of the conveyor rope, which is especially likely during winter thunderstorms.

[0058] The proposed energy-autonomous operation of the detection device according to the invention without galvanic connection to a power supply network has the advantage that no separation distances to the measuring device need to be maintained.

[0059] The use of the presented device according to the invention aims at the detection and classification of lightning and overcurrent events, including those not caused by lightning impulse currents but exhibiting an impulse current character in the range of > 50 A up to 200 kA, and at the detection of events of pulse shapes as long-term pulses with T ≥ 10 ms as well as pulse shapes of 10 / 350 µs and 8 / 20 µs.

[0060] The invention will be explained in more detail below with reference to an exemplary embodiment and to figures.

[0061] The Figure 1Figure 1 shows a basic arrangement of the device according to the invention with, for example, three reed contacts at a defined distance from the electrical conductor.

[0062] The Figure 2 Figure 1 shows a simplified block diagram of the evaluation electronics with a low-pass filter 90 downstream of the respective reed sensor 4; 5; 6, the respective output of which leads to a microcontroller 100, which is connected on the output side to a radio interface 110.

[0063] In the block diagram according to Figure 3 The system again uses reed sensors 4; 5; 6, which are connected to an RC low-pass filter 90.

[0064] To determine the switching time of the respective reed sensor 4; 5; 6, the low-pass filters are each connected to the input of a comparator 120, the output of which leads to the microcontroller 100 and memory unit.

[0065] In this regard, a timer module 130 is provided, which leads to the comparison input of the comparator 120. The power supply is provided by the [unclear - possibly referring to a specific component or device]. Figure 1 The previously described battery 5 is used. With the help of the timing module 130 and the microcontroller 100, the detected pulse shape can be determined from the switching time of the respective reed sensor or reed contact 4; 5; 6 using signal processing technology.

[0066] The modules 110 and 140 form an air interface and ensure wireless data transmission of the detected surge current quantities.

[0067] Another signal processing and control unit 150 is connected to a communication module 160 to ensure cloud connectivity via GSM. Alternatively, a conventional internet connection for data evaluation and long-term analysis can be implemented using module 170.

[0068] The device according to the exemplary embodiment according to Figure 1starts with a circuit board 1, which has an evaluation unit with radio module 2 and a long-term stable power supply in the form of a battery 3.

[0069] Three spaced-apart reed contacts 4, 5 and 6 are arranged on a flat side section of the printed circuit board 1 or wiring carrier, and are essentially parallel to each other. At least one of the reed contacts can be shielded to adjust the response behavior.

[0070] An electrical conductor 8 is brought into contact with a quasi-stop edge 7 of the circuit board 1. This could, for example, be a conductor cable of a wind turbine rotor.

[0071] When the current-carrying conductor 8 is subjected to an impulse current, a magnetic field is formed around the conductor, which penetrates the spaced-apart reed contacts 4, 5, 6 to varying degrees.

[0072] For example, it is assumed that reed contact 4 has a distance of 5 mm from the conductor, reed contact 5 has a distance of 15 mm from the conductor, and reed contact 6 has a distance of 105 mm from the conductor.

[0073] The reed contact 4 is capable of detecting long-term pulses with an impedance ≥ 50 A and a pulse duration of T ≥ 10 ms. Likewise, the reed contact 4 located at the closest distance to the surge arrester 8 can detect surge current pulses of the 10 / 350 µs pulse shape with an impedance ≥ 60 A and surge current pulses of the 8 / 20 µs pulse shape with an impedance ≥ 70 A.

[0074] The reed contact 5 is able to detect pulse currents of the pulse shape 10 / 350 µs with Imin ≥ 200 A and pulse currents 8 / 20 µs with Imin ≥ 750 A.

[0075] The reed contact relay 6, located at a distance of approximately 105 mm from the conductor cable 8, is capable of detecting pulses of the pulse shape 10 / 350 µs with Imin ≥ 4.5 kA and pulses of the pulse shape 8 / 20 µm with Imin ≥ 67 kA.

[0076] With the help of the evaluation electronics integrated in the device, the different switching times of the reed contacts can be recorded and evaluated depending on the pulse shape, so that it is possible to identify which pulse shapes with which pulse duration are involved.

[0077] Likewise, by selectively responding to corresponding surge currents, a distinction can be made in the range of approximately 60 A up to 250 kA.

[0078] In the event of a lightning or surge current, this is initially detected by the activation of at least one reed switch. The measured current intensities are then differentiated based on the response behavior of the individual reed switches. The recorded data, taking into account the time course and the time delta to subsequent events, are stored and are then available for further analysis.

[0079] With a device according to the invention tested in the test field, the minimum detectable current is approximately 45 A. By using, for example, three reed contacts, three pulse thresholds can be defined and evaluated. Further diversification is possible with a corresponding extension of the microcontroller used for evaluation, without departing from the basic principle of the invention.

[0080] Components that may be required for long-term storage and analysis of the recorded values ​​can be installed in EMC-protected areas, spatially separated from the device according to the invention. This is possible because the measured values ​​provided by the device are preferably transmitted wirelessly to the downstream evaluation unit, and this transmission can only be triggered after the last disturbance event has subsided.

[0081] By setting a fixed delay time between the occurrence of a lightning event and the sending of the event log, a millisecond-accurate time assignment or a millisecond-accurate timestamp can be achieved.

[0082] The following exemplary trigger thresholds for the reed contacts were obtained after the tests were carried out: Table 1: Trigger thresholds of the reed contacts Pulse shape reed 1 reed2 reed3 8 / 20 µs 350 A 1250 A 67kA 10 / 350 µs 140 A 260 A 4.5kA DC test field 141 A - -

[0083] The tripping thresholds of the reed contacts can be significantly varied by the spacing and type of contacts. These tripping thresholds can differentiate between a constant current (Icc only) and a short-term pulse. If the third reed contact is to trip at a higher current, the spacing can be increased further. A deviation in the tripping threshold of 10 A was observed for the different conductor lengths (95 mm², Ø = 11 mm, insulation thickness = 2.5 mm; 50 mm², Ø = 8 mm, insulation thickness = 2.5 mm). The tripping threshold is significantly lower with 10 / 350 pulses compared to 8 / 20 pulses.

[0084] Among other things, the following dependency of the response from a certain distance to the guide wire can be observed between the trigger thresholds of the unshielded reed contacts of the 8 / 20 and 10 / 350 µs pulses. ∫ I 8 / 20 t 2 dt ∫ I 10 / 350 t 2 dt ≈ 15

[0085] According to the Figure 4A current-carrying rope or conductor 8 is shown schematically with the surrounding magnetic field lines B. The corresponding reed switch 9 is radially oriented to the magnetic field of the conductor 8 such that its terminals and contacts are exposed to the magnetic flux density B. When the response flux density or the magnetic sensitivity of the reed switch 9 is reached, the contacts close.

[0086] The achievement of the response flux density of the reed contact 9 depends on the current in the rope 8, the distance of the reed contact 9, the sensitivity of the reed contact 9 and the alignment of the reed contact 9 to the conductor rope 8.

[0087] Furthermore, the response behavior can be changed by influencing the magnetic flux B, for example by introducing materials with higher permeability.

[0088] In the Figure 4The magnitude of the magnetic flux density as a function of the distance R to the central axis of the conductor 8 is shown in principle. The axes shown are to be understood as logarithmic. The minimum distance of the reed contact 9 is limited here by the geometry of the conductor 8 and the necessary, possibly insulated, mounting. Figure 4 Line 10 represents the magnetic flux density for a high current, and line 11 for a lower current. Line 13 indicates the response threshold of a low-sensitivity reed contact 9, and line 12 of a sensitive reed contact 9.

[0089] With a small current flow and correspondingly low magnetic flux density 11 through the conductor 8, the response threshold of a low-sensitivity reed switch 9 13 is not reached, even at the minimum technically feasible distance between the reed switch 9 and the conductor 8. Under these circumstances, current detection does not occur. To nevertheless achieve detection with such a reed switch 9, it is possible to increase the concentration of the magnetic field lines, for example, by using ferromagnetic materials that coaxially surround the conductor 8 in certain areas and are connected to the terminals of the reed switch.

[0090] However, such an arrangement can be complex and can potentially be avoided by using a more sensitive reed switch (line 12). Such a switch can detect the corresponding current or its magnetic flux density even at distances of a few millimeters or centimeters. Only at greater distances does the magnetic flux density of the current (line 11) fall below the sensitivity of a corresponding reed switch (line 12), at which point detection may no longer be possible.

[0091] At high currents, however, the magnetic flux density (line 10) remains far above the high sensitivity of the reed switch (line 12) even over considerable distances. Such distances are often impractical for technical applications due to the limited size of the devices.

[0092] The sensitivity range of available reed switches is limited. A further disadvantage is that the response time of reed switches generally increases with decreasing sensitivity, meaning that the desired detection of short-duration pulse currents is either impossible or only possible with significant time delays.

[0093] However, the magnetic flux density of long-term currents of a few tens of amps and impulse currents of several hundred kiloamps differs greatly, so that even with insensitive sensors, the necessary distances are considerable and can amount to several meters if high detection thresholds are desired for lightning currents, resulting in limitations in use.

[0094] To achieve high current thresholds for impulse currents, and especially lightning currents with a pulse shape of 10 / 350 µs, in compact devices, the sensors can be equipped with complete or partial shielding. For oriented sensitivity, the shielding can also have windows. The shielding thus has a weakening or a recess through which the magnetic field can partially penetrate.

[0095] According to Figure 5 The functionality of the aforementioned shielding is explained using an example.

[0096] The diagram shows the distance r SW of the sensor 9 to the conductor cable 8 in millimeters, up to which an unshielded reed contact 9 with a sensitivity of approximately 15 AT closes depending on the magnitude of the lightning currents.

[0097] An experimentally determined curve with recorded measurement points (gray tone) for the unshielded reed contact 9 clearly shows that, for desired threshold values ​​of 200 kA or higher, the reed contact would have to be installed at a distance of several meters from the conductor cable.

[0098] It becomes clear that even with relatively low lightning currents of only 20 kA, a considerable distance of approximately 75 cm would have to be maintained if one wanted to detect the exceedance of such a current level in the conductor cable 8.

[0099] For very high current thresholds, a compact measuring arrangement, or one constructed within a housing, is therefore difficult to implement. Reed contacts with higher insensitivity only shift these distances slightly and have the disadvantage of the timing of their closing relative to the actual current event. Positioning and mounting the reed contact in a less sensitive position relative to the conductor cable is very critical and places very high design demands on the construction and installation of such devices.

[0100] According to Figure 5A structurally identical reed switch is used, for example, with a steel tube with a wall thickness ranging from one to a few millimeters. This is simplified by reference numeral 14. Arrow 15 shows the effect of this simple arrangement and distance at which the current source (current > 50 kA 10 / 350 µs) can be detected. From a distance of approximately 2 m for the unshielded reed switch or sensor, the distance shifts to just a few millimeters or centimeters.

[0101] For even higher impulse currents, a double 16 or triple shielding 17 can be used instead of a single shielding.

[0102] In this case, the shielding and steel pipes are separated by insulated intermediate layers or air.

[0103] In these examples, with the same reed contact, the distance for detecting the threshold values ​​of current > 100 kA or > 150 kA is reduced from a range of several meters to a few centimeters.

[0104] It becomes clear that very compact devices for detecting a wide range of current thresholds can be realized by utilizing the concept of shielding. Reed contacts, or sensors used in this way, can be designed for a multitude of different impulse current thresholds by employing different shielding materials, provided the same reed contacts and the same distance to the conductor cable are used.

[0105] Additionally, the shielding can be partially reduced or an opening can be introduced into the shielding. A grid-like or mesh-like shielding could also be used. This measure not only allows for directional characteristics but also influences the sensitivity, even with the same shielding geometry.

[0106] The shielding 18, which basically corresponds to the geometry of the simple shielding 14, was provided with a partial opening, whereby in the Figure 5 A current threshold of 20 kA can be detected at a distance of a few millimeters. Using simple shielding without attenuation 14, this current threshold might not be technically achievable due to the excessive shielding.

[0107] The shielding effect of a ferromagnetic material is based on the higher permeability of the shielding material. The magnetic field lines are deflected until the material reaches saturation, which significantly weakens the magnetic field in the area of ​​the reed contacts and thus prevents the reed contacts from closing until the shield reaches saturation.

[0108] In addition to the selection of the ferromagnetic material or the combination of such materials and their magnetic properties, the effect of the shielding can be influenced by the geometry and the positioning of the reed contact in the shielding.

[0109] This results in a multitude of possibilities for using the shielding for the purpose of using reed contacts for the task of detecting and evaluating long-term currents or impulse currents in compact devices or arrangements.

Claims

1. A device for detecting electrical currents on or in the vicinity of electrical conductors (8) with at least one reed contact (4; 5; 6; 9) as a magnetically responsive switch, which is arranged in the vicinity of the electrical conductor (8) such that, when there is a significant current flow through the electrical conductor (8), the developing magnetic field triggers the switch and initiates an evaluation electronics connected to the switch, wherein for detecting surge current variables and differentiating long-term pulse currents, on the one hand, and short-time pulse currents, on the other, a plurality of reed contacts (4; 5; 6; 9) is arranged in a predefined distance from the electrical conductor (8), wherein the evaluation electronics (2) determines the response and the switching times of the respective reed contacts (4; 5; 6; 9), from the allocation of the determined values to the respective reed contact (4; 5; 6; 9), the surge current variable is detected, and from the switching time, the pulse shape is detected, characterized in that for setting the response behavior, at least one of the reed contacts (4; 5; 6; 9) has a shield (14; 16; 17; 18) for influencing the magnetic field (B) acting upon the respective reed contact (4; 5; 6; 9), wherein the shield (14; 16; 17; 18) prevents a closing of the at least one reed contact (4; 5; 6; 9) until the saturation of the shield (14; 16; 17; 18) is reached.

2. The device according to claim 1, characterized in that the electrical conductor (8) is an integral part of a lightning current arresting system or an arrester rod.

3. The device according to claim 1, characterized in that the electrical conductor (8) is an integral part of a surge current-carrying overvoltage arrester.

4. The device according to any one of the preceding claims, characterized in that the evaluation electronics (2) has a microcontroller (100) and at least one low-pass filter (90).

5. The device according to claim 4, characterized in that the data is transferred in a wireless or wired manner to a superordinate unit for long-term analysis of pulse-shaped surge currents.

6. The device according to claim 4 or 5, characterized in that a radio module (111; 140) is provided for data transmission, wherein the data transmission is only triggered after expiration of a predetermined period of time after the last surge current pulse has decayed.

7. The device according to any one of the preceding claims, characterized in that it has an autonomous long-term current supply (3; 50).

8. The device according to any one of the preceding claims, characterized in that at least the reed contacts (4; 5; 6; 9) are fixed on a planar wiring carrier.

9. The device according to claim 8, <b>characterized in that the angular position of the groups of reed contacts (4; 5; 6; 9) with respect to the electrical conductor (8) is fixedly predefined.

10. The device according to any one of the preceding claims, characterized in that a housing accommodating the components of the device is formed, which housing has a front or side surface provided with means for identifying the position of and / or attaching the electrical conductor (8).

11. The device according to any one of the preceding claims, characterized in that it is in each case arranged on or in the vicinity of lightning arrester cables of rotor blades in wind turbines.

12. The device according to any one of the preceding claims, characterized in that after expiration of a predetermined or settable period of time between the pulse event and data transferal, a time stamp can be generated.

13. The device according to any one of the preceding claims, characterized in that the electrical conductor (8) is an integral part of constructional parts or facilities that do not carry lightning current, in particular of hoisting cables or carrier cables of cableways or cranes.

14. Use of a device according to one or more of claims 1 to 11 for detecting and classifying lightning current and overcurrent events having a surge current character in the range from < 50 A to 200 kA and pulse shapes as a long-term pulse with T ≥ 10 ms as well as pulse shapes of 10 / 350 µs and 8 / 20 µs.